32,335,648 deliveries · 2016–2024 · observed rates, not predictions
1. Robson groups. Every delivery, every gestation and presentation, classified into the ten groups. Gives the standard ten-group table for any combination of maternal age, pre-pregnancy body mass index, race and Hispanic origin, and payment source: size of group, cesarean rate in group, and absolute contribution to the stratum rate.
2. Term cesarean rate. Singleton, cephalic, 37 to 41 completed weeks. Gives the observed cesarean rate for any combination of parity, previous cesarean, completed week, induction, body mass index, maternal age, race and Hispanic origin, and payment source.
Both open with every menu on Any and narrow only where you choose.
Every figure is a direct count from the National Vital Statistics System natality files. Nothing is modelled, fitted, smoothed or extrapolated. Choose a combination and the tool sums the matching birth records and divides.
Because the classification is applied to routinely collected data rather than to a research cohort, group sizes should be read before any rate, and differences between strata should be attributed first to data quality, then to epidemiological variables, and only then to clinical practice.
United States 2016–2024 · NVSS natality microdata · observed rates, not predictions
All deliveries, every gestation and presentation, classified into the Robson Ten Group Classification System. 32,335,648 deliveries.
Size of group is deliveries in the group over all deliveries in the stratum. Contribution is cesareans in the group over all deliveries in the stratum; it is the absolute contribution, and the thirteen contributions sum to the stratum cesarean rate. Robson's rule: read the group sizes before any rate.
Groups 2b and 4b are prelabor cesarean by definition, so their rate is 100 per cent. Group 9 rests on a birth-certificate presentation code of Other, which is not restricted to transverse and oblique lie, and should not be read as a clean abnormal-lie group. Unclassified is a data-quality indicator, not a clinical group.
Group sizes and rates by single year for the stratum selected above. A single year's fluctuation is not a trend; 2020 and 2021 are pandemic years.
Payment source is shown beside race on every result because the two are deeply confounded in United States birth data, and a race-specific rate read without the payer distribution invites the wrong conclusion.
Singleton, cephalic, 37–41 completed weeks. 24,829,712 deliveries. Cesarean rate for any combination of eight characteristics.
A prelabor cesarean is recorded as a cesarean with no trial of labor attempted, so those women never entered labor. The left figure is the rate among only the women who did labor; it is the number relevant to a woman who is expected to labor. The right figure is the share of the whole cell delivered without labor.
Each table varies one characteristic and holds the rest at whatever the menus say, Any included. The two rows above differ in recorded labor onset only. They are not a treatment comparison: women selected for induction differ from women who labor spontaneously in ways birth certificates do not capture.
Payment source is shown on every result because race and payer are deeply confounded in United States birth data, and a race-specific rate read without the payer distribution beside it invites the wrong conclusion.
Obesity is split into class I, class II and class III rather than pooled above 30, because the cesarean gradient continues to rise across those three classes and a single “30 or more” category conceals it.
Nine single years of a fixed cohort. A single year's fluctuation is not a trend; look for sustained directional change across three years or more, and read 2020 and 2021 as pandemic years rather than ordinary observations.
Every publication, definition and exclusion behind the figures
Robson group explorer. All hospital deliveries with a birthweight of 500 g or more, every gestation and presentation, 32,335,648 deliveries. Nothing is excluded for a missing characteristic; Unknown is carried as a level in the body mass index, race and payment menus, so selecting Any everywhere reproduces the published all-deliveries table exactly.
Term cesarean rate calculator. Hospital deliveries with a birthweight of 500 g or more, singleton, cephalic presentation, 37 to 41 completed weeks by the obstetric estimate, 24,829,712 deliveries. 3.7 per cent of otherwise eligible deliveries are excluded there because one of the eight characteristics is missing or not stated, most often body mass index.
The unit is the delivery, not the infant. A twin pregnancy is one delivery, not two, because the denominator of the classification is the woman. The natality file holds one record per infant, so one record per delivery is selected as every singleton plus the first infant of each multiple set (SETORDER_R = 1). Counting infants would double group 8 and dilute the size and contribution of every other group.
Parity is the live birth order recode, so parity 0 is nulliparous. Previous cesarean is the birth-certificate risk-factor item. Induction is the birth-certificate labor-characteristic item. A prelabor cesarean is a cesarean recorded with no trial of labor attempted; because those women never laboured, the term calculator reports the cesarean rate twice, once among all women in the cell and once among only those who laboured.
In strict order: plurality greater than one to group 8, any multiple including quintuplet or higher; singleton with presentation coded Other to group 9; singleton breech to group 6 if nulliparous and group 7 if multiparous; singleton cephalic at 36 weeks or less to group 10; term singleton cephalic with a previous cesarean to group 5; and the remaining term singleton cephalic pregnancies to groups 1, 2a and 2b if nulliparous and to groups 3, 4a and 4b if multiparous, by labor onset. Where induction and no trial of labor were both recorded, which is a logical contradiction, induction takes precedence.
Subgroups follow Robson: 2a and 4a are induced labor, 2b and 4b are prelabor cesarean. The correct denominator for the induction rate in group 2 is groups 1 and 2 combined, and for group 4 it is groups 3 and 4 combined, never the group alone.
Size of group is deliveries in the group over all deliveries in the stratum. Cesarean rate in group is cesarean deliveries in the group over deliveries in the group. Contribution is cesarean deliveries in the group over all deliveries in the stratum; it is the absolute contribution, and the thirteen contributions sum to the stratum cesarean rate.
Group sizes should be read before any rate. No group can be interpreted on its own until the relative sizes of the others in the same stratum have been read. Groups 6 to 10 always carry high cesarean rates and always contribute little, because they are small.
Group 9 is defined by a presentation code of Other, which on the birth certificate is not restricted to transverse and oblique lie. Its cesarean rate falls from 58.1 per cent in 2016 to 46.5 per cent in 2024, which is not a plausible clinical trajectory for a true abnormal-lie group and points to abstraction drift. It should not be read as a clean abnormal-lie group.
Groups 2b and 4b are derived rather than recorded. The prelabor cesarean share in United States data has been questioned in print as implausibly high and possibly a misclassification artifact of deriving labor onset from the trial-of-labor item. Those figures should not be read at face value.
Previous cesarean is a self-reported birth-certificate item and is the sole determinant of group 5. Between 884 and 1,117 records a year are coded nulliparous with a previous cesarean; they are assigned to group 5 on the previous-cesarean criterion.
Body mass index derives from self-reported pre-pregnancy weight and height and is missing for 1.9 to 2.7 per cent of records depending on the year. The cesarean status of a multiple delivery is taken from the first-born infant, so a combined vaginal-cesarean delivery is counted as vaginal, which understates the group 8 cesarean rate by roughly 1.4 percentage points.
The user guide lists the plurality field as running from 1 to 4, but the file also contains the value 5. Bounding the group 8 rule at 4 silently drops those records; the rule used here has no upper bound.
Resident birth totals and the overall cesarean rate reproduce the published National Center for Health Statistics final figures for every year from 2016 to 2024. Every characteristic reproduces the published national distribution: 39 weeks is the modal term week at 37.2 per cent, induction runs at 32.8 per cent, Medicaid at 41.1 per cent, Hispanic origin at 25.0 per cent. The two explorers were built by separate extraction passes over the microdata and reproduce each other's group totals exactly.